This is the act of, when masturbating in bed, turning on to your side and jizzing all over what is next to you (eg. empty side of double bed, floor, girlfriend, Justin Bieber poster) After completion then roll back onto your back and be happy as no cleanup operation is required. Popular amongst members of the Royal Navy because bog roll is in short supply on ships and Navy birds are ugly. Under no circumstances attempt happy rolling in a sleeping bag.
Dude your room smells like youve been happy rolling in here for a month, and since when did Justin Bieber grow a yellow goatee?